We created datacubes without spectral averaging, i.e. keeping the native spectral resolution of \(\sim \) 10 km s\(^{-1}\) .
The visibilities from the two configurations, which were calibrated using the CASA 5.4.0 software [1]} in the pipeline mode, were combined for all sources except for J1010, which was observed in the compact configuration only. Moreover, visibilities from all spectral windows were averaged to measure the mm continuum emission, by excluding the spectral region associated with the CO(2\(-\) 1) emission line (|v-v\(_{\rm sys}\) |\(<\) 500 km s\(^{-1}\)  for J1100, J1010 and J1509, and |v-v\(_{\rm sys}\) |\(<\) 600 km s\(^{-1}\)  for the other QSO2s). To model the continuum emission next to the line, we fitted a first order polynomial in the uv plane to channels with velocities 500(600)\(<\) |v-v\(_{\rm sys}\) |\(<\) 2000 km s\(^{-1}\) . The subtraction of this fit provided us with continuum-subtracted visibilities. We thus produced continuum-subtracted data-cubes by using the tclean CASA task in non-interactive mode, using natural weighting. The Hogbom cleaning algorithm was used in combination with a threshold of three times the rms sensitivity. Similarly, imaging of continuum maps was performed. The resulting rms sensitivity and beamsize of our QSO2 observations are listed in Table REF . In addition to the rms noise, there is a 10% flux calibration error.
We note that the combination of the C43-3 and C43-6 configurations allowed us to reach angular resolutions of \(\sim \) 0.18–0.25 (300–500 pc at z\(\sim \) 0.1), while recovering extended emission on scales of up to \(\sim \) 6.5–8.6 (12–16 kpc). Such combination was fundamental to recover the total CO emission of the QSO2s.
As shown in Section REF , four of the QSO2s have APEX CO(2–1) luminosities measured in an aperture of \(\sim \) 28 [2]}, which we have compared with our total CO fluxes (see Section REF ).
